A humanized mouse model of b-islet cell autoimmunity. The goal of this proposal is to produce a mouse model on a diabetes permissive murine background with a humanized CD4 T cell compartment, in which to study different approaches towards controlling b-islet cell specific autoimmunity. Due to significant differences in the chaperone function of the murine and human invariant (li) species, the HLA class II transgenic mice, are also being supplied with a human li transgene (hu-li) and a gene knock out for the murine li. Since neither of the two murine Proinsulin (P-lns) varieties (P- Ins1 or P-lns2) contain the major (C-peptide/A-chain) CD4 T cell epitope previously identified in both HLA- DR*0401 transgenic mice and HLA-DR*0401 positive T1D patients, a correctly expressed human preproinsulin transgene (hu-PPI) is also being added. Existing immuno-competent HLA-DR*0401, DQ8, hu- CD4, Ab-/-, NOD mice are being crossed with new humanized li and P-lns transgenic NOD mice. In order to examine the effects of humanizing the li and the Preproinsulin species, the humanized mice, in which human Proinsulin is now a self-protein, will be used to study T cell receptor repertoires and cytokine responses after immunization with human P-lns. We believe that these mice could be key players in pre-testing new islet specific vector based immuno-therapies in T1D. The proposal outlines how to obtain a similarly humanized immuno-deficient mouse model on a NOD background also carrying the Rag-/-, gc-/- double knock out, in which to study the development, maturation, and distribution of a functional immune system after transfer of histo-compatible green fluorescent protein (GFP) labeled murine HSC. These mice will also be ideal recipients for adoptive transfer of GFP labeled potentially autoreactive CD4 &CDS T cell populations triggering disease in the humanized mouse model of T1D. Finally, the proposal suggests to use the immuno- deficient version of the humanized mouse model to examine the different conditions for induction of active immunity versus tolerance in "vaccination studies", where human Proinsulin producing dendritic cells (DC) will be co-transferred with different CD4 and/or CDS T cell populations into histocompatible mice carrying the diabetes susceptible HLA-DR*0401, DOS alleles, a humanized li species, as well as, a correctly expressed human P-lns transgene.